﻿// Copyright (c) 2011 AlphaSierraPapa for the SharpDevelop Team
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Threading;
using ICSharpCode.Decompiler;
using ICSharpCode.TreeView;

namespace ICSharpCode.ILSpy.TreeNodes
{
	/// <summary>
	/// Adds threading support to nodes
	/// </summary>
	class ThreadingSupport
	{
		Task<List<SharpTreeNode>> loadChildrenTask;
		CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
		
		public bool IsRunning {
			get { return loadChildrenTask != null && !loadChildrenTask.IsCompleted; }
		}
		
		public void Cancel()
		{
			cancellationTokenSource.Cancel();
			loadChildrenTask = null;
			cancellationTokenSource = new CancellationTokenSource();
		}
		
		/// <summary>
		/// Starts loading the children of the specified node.
		/// </summary>
		public void LoadChildren(SharpTreeNode node, Func<CancellationToken, IEnumerable<SharpTreeNode>> fetchChildren)
		{
			node.Children.Add(new LoadingTreeNode());
			
			CancellationToken ct = cancellationTokenSource.Token;
			
			var fetchChildrenEnumerable = fetchChildren(ct);
			Task<List<SharpTreeNode>> thisTask = null;
			thisTask = new Task<List<SharpTreeNode>>(
				delegate {
					List<SharpTreeNode> result = new List<SharpTreeNode>();
					foreach (SharpTreeNode child in fetchChildrenEnumerable) {
						ct.ThrowIfCancellationRequested();
						result.Add(child);
						App.Current.Dispatcher.BeginInvoke(DispatcherPriority.Normal, new Action<SharpTreeNode>(
							delegate (SharpTreeNode newChild) {
								// don't access "child" here the
								// background thread might already be running the next loop iteration
								if (loadChildrenTask == thisTask) {
									node.Children.Insert(node.Children.Count - 1, newChild);
								}
							}), child);
					}
					return result;
				}, ct);
			loadChildrenTask = thisTask;
			thisTask.Start();
			thisTask.ContinueWith(
				delegate (Task continuation) {
					App.Current.Dispatcher.BeginInvoke(DispatcherPriority.Normal, new Action(
						delegate {
							if (loadChildrenTask == thisTask) {
								node.Children.RemoveAt(node.Children.Count - 1); // remove 'Loading...'
							}
							if (continuation.Exception != null) { // observe exception even when task isn't current
								if (loadChildrenTask == thisTask) {
									foreach (Exception ex in continuation.Exception.InnerExceptions) {
										node.Children.Add(new ErrorTreeNode(ex.ToString()));
									}
								}
							}
						}));
				});
			
			// Give the task a bit time to complete before we return to WPF - this keeps "Loading..."
			// from showing up for very short waits.
			thisTask.Wait(TimeSpan.FromMilliseconds(200));
		}
		
		public void Decompile(Language language, ITextOutput output, DecompilationOptions options, Action ensureLazyChildren)
		{
			var loadChildrenTask = this.loadChildrenTask;
			if (loadChildrenTask == null) {
				App.Current.Dispatcher.Invoke(DispatcherPriority.Normal, ensureLazyChildren);
				loadChildrenTask = this.loadChildrenTask;
			}
			if (loadChildrenTask != null) {
				foreach (ILSpyTreeNode child in loadChildrenTask.Result.Cast<ILSpyTreeNode>()) {
					child.Decompile(language, output, options);
				}
			}
		}
		
		sealed class LoadingTreeNode : ILSpyTreeNode
		{
			public override object Text {
				get { return "Loading..."; }
			}
			
			public override FilterResult Filter(FilterSettings settings)
			{
				return FilterResult.Match;
			}
			
			public override void Decompile(Language language, ITextOutput output, DecompilationOptions options)
			{
			}
		}
		
		sealed class ErrorTreeNode : ILSpyTreeNode
		{
			readonly string text;
			
			public override object Text {
				get { return text; }
			}
			
			public ErrorTreeNode(string text)
			{
				this.text = text;
			}
			
			public override FilterResult Filter(FilterSettings settings)
			{
				return FilterResult.Match;
			}
			
			public override void Decompile(Language language, ITextOutput output, DecompilationOptions options)
			{
			}
		}
	}
}
